Abstract Book

S1146

ESTRO 37

Conclusion For most patients, respiratory-induced diaphragm motion estimated from a single pre-treatment 4D-CT was not representative for respiratory-induced diaphragm motion during treatment. Respiratory-induced diaphragm motion is very variable and not well predicted by a single measurement. Hence, when respiratory-induced target motion is expected, an adaptive treatment strategy is necessary for radiotherapy in children. EP-2088 Quantification of image quality parameters of dual energy CT using software for quality control B. Pawalowski 1,2 , H. Szweda 1 , D. Radomiak 1 , K. Matuszewski 1 , U. Sobocka- Kurdyk 3 , A. Skrobala 1,4 , T. Piotrowski 1,4 1 Greater Poland Cancer Centre, Medical Physics Department, Poznan, Poland 2 Poznan University of Technology, Department of Technical Physics, Poznan, Poland 3 Greater Poland Cancer Centre, Medical Physics Department, Kalisz, Poland 4 Poznan University of Medical Science, Department of Electroradiology, Poznan, Poland Purpose or Objective The first aim of this study was to perform quantification analysis of low contrast resolution and corresponding parameters like signal to noise ratio (SNR) and noise of dual energy CT using CATPHAN phantom and ARTISCAN software. The second aim was to determine the optimal parameters for the best image quality of monoenergetic scans. Material and Methods The ability of dual-energy computed tomography (CT) to differentiate materials with similar CT number but different atomic composition makes this method very interesting for many clinically applications. Dual-energy CT could also improve quality of images like low contrast, signal to noise ratio and noise. To evaluate this image quality parameters two sets of CATPHAN phantom scans using dual-energy mode (80 and 140 keV) were acquired on CT Siemens Definition AS. This phantom has special modules for low contrast, SNR and noise evaluation. Low contrast module has three sets of discs with different contrast (1%, 0.5% and 0.3%). Furthermore each sets has 9 discs with different diameter (2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 15 mm). Then sixteen monoenergetic series were created using dedicated software from Siemens. Scans were created every 10 keV from 40 keV to 190 keV. Next the ARTISCAN software from Aquilab was used for analysis. This software using mathematical formulas provide quantitative information about detected and undetected disc, SNR and noise. For all scans low contrast resolution, signal to noise ratio and noise was computed and compared between each monoenergetic series. Results All monoenergetic series were analyzed using ARTISCAN software. This program provides quantitative and objective analysis of evaluated parameters. For every sets low contrast resolution, signal to noise ratio (SNR) and noise were computed and evaluated. The low contrast resolution is defined as the diameter of the smallest detected object. Therefore the number of detected disc was evaluated. The best low contrast resolution was obtained for 60 keV and 70 keV. Table 1 presents detected and undetected disc and low contrast resolution expressed as diameter of the smallest detected disc. Next evaluated parameter was signal to noise ratio. The highest and therefore the best value was obtained for 60 keV and was 315 a.u. For comparison median value for SNR was 107 a.u. for all energies. Also for the calculated noise the smallest value therefore the best was for 60 keV and was 0,42%. For comparison the

continues by verifying feasibility of the method for targets located anywhere in the body and treated either with photons or protons. EP-2087 Can respiratory-induced diaphragm motion in children be reliably estimated from a single 4D-CT? S. Huijskens 1 , I.W.E.M. Van Dijk 1 , J. Visser 1 , B.V. Balgobind 1 , C.R.N. Rasch 1 , A. Bel 1 1 Academic Medical Center, Radiation Oncology, Amsterdam, The Netherlands Purpose or Objective In adults, a single pre-treatment four-dimensional CT (4D-CT) acquisition is often used to account for respiratory-induced target motion during radiotherapy. However, studies have indicated that a 4D-CT is not always representative for respiratory motion. Paediatric data on respiratory-induced target motion during radiotherapy is limited. Our aim was to investigate if respiratory-induced diaphragm motion during radiotherapy in children can be reliably estimated from a single pre-treatment 4D-CT. Material and Methods To investigate the predictive value of a 4D-CT for respiratory-induced diaphragm motion (as a surrogate for target motion), nine patients (mean age 14yrs; range 8.5– 17.9yrs) were retrospectively included when the diaphragm was visible on upper abdominal or thoracic free breathing imaging data. From each patient, a 4D-CT for planning purposes, and daily/weekly CBCTs (total 102; range 4–32 per patient) acquired prior to dose delivery were available. For each CBCT, a two- dimensional Amsterdam Shroud image was created, allowing for selection of the cranial-caudal position of the end-inspiration and end-expiration positions of the top of the right diaphragm dome. Pixel coordinates were corrected for the scanner geometry and translated into millimetres relative to the patients’ isocenter. The mean peak-to-peak amplitude was defined as the average displacement between end-inspiration and end-expiration diaphragm positions. Additionally, the peak-to-peak diaphragm motion, corresponding to the difference in position of the diaphragm in end-inspiration and end- expiration phases, was extracted from the 4D-CTs, and compared to the distributions of diaphragm motion in CBCTs (one-sample t-test). Results On average, peak-to-peak diaphragm motion over all CBCTs was 9.6 mm, and peak-to-peak diaphragm motion in 4D-CT was 9.3mm. For 7 out of 9 patients, peak-to- peak diaphragm motion on 4D-CT differed significantly (p<0.05) from diaphragm motion on CBCT (Figure 1). Differences >3mm were found in 60 of the 102 fractions (59%), mostly with 4D-CT underestimating daily/weekly respiratory-induced diaphragm motion.